Tn5cos: a transposon for restriction mapping of large plasmids using phage lambda terminase.

A method for the rapid restriction mapping of large plasmids has been developed. A 400-bp fragment of phage lambda DNA containing the cos region has been inserted into Tn5. After in vivo transposition of this Tn5cos element into the plasmid of choice, the plasmid is isolated and linearized at its cos site with phage lambda terminase (Ter). Such Ter linearization was about 70% efficient. After partial digestion of the linear molecules with the appropriate restriction enzyme, the products are selectively labelled at the right or left cohesive phage lambda DNA termini by hybridization with digoxygenin (DIG)-11-dUTP-labelled (using terminal transferase) oligodeoxyribonucleotides complementary to the single-stranded cos ends. After pulsed field gel electrophoresis, the labelled fragments are visualized in the dried gel using a DIG-detection kit. The restriction map can be directly determined from the 'ladder' of partial digestion products.     

Fingerprinting of bacterial genomes by amplification of DNA fragments surrounding rare restriction sites.

A method for generating limited representations of total bacterial DNA, without prior knowledge of the DNA sequence, has been developed. This method consists of three steps: digestion with two restriction enzymes, ligation of two oligonucleotide adapters corresponding to the restriction sites, and selective PCR amplification of the ligation products. The method relies on the use of two restriction enzymes with considerable differences in cleavage frequency of the investigated DNA and the ligation of two different oligonucleotides, each corresponding to one of the two cohesive ends of DNA fragments. Three subsets of DNA fragments are generated during digestion and subsequent ligation: terminated with the same oligonucleotide on both 5' ends of DNA fragments (two subsets) and terminated with two different oligonucleotides. Suppression PCR allows only the third subset of DNA fragments to be amplified exponentially. The method allows bacterial species strain differentiation on the basis of the different DNA band patterns obtained after electrophoresis in polyacrylamide gels stained with ethidium bromide and visualized in UV light.     

Physical characterization of SCP1, a giant linear plasmid from Streptomyces coelicolor.

SCP1, coding for the methylenomycin biosynthesis genes in Streptomyces coelicolor, was shown to be a giant linear plasmid of 350 kb with a copy number of about four by analysis with pulsed-field gel electrophoresis. A detailed physical map of SCP1 was constructed by extensive digestion with six restriction endonucleases, by DNA hybridization experiments, and finally by cloning experiments. SCP1 has unusually long terminal inverted repeats of 80 kb on both ends and an insertion sequence at the end of the right terminal inverted repeat. Analysis by pulsed-field gel electrophoresis in agarose containing sodium dodecyl sulfate revealed that a protein is bound to the terminal 4.1-kb SpeI fragments derived from both ends of SCP1. Treatment with lambda exonuclease or exonuclease III and SpeI digestion also indicated that the 5' ends of SCP1 are attached to a protein.     

Ultraviolet irradiation of DNA: a way of generating partial digests for rapid restriction site mapping

UV-irradiation of DNA can inhibit the activity of certain restriction endonucleases because of thymine dimer formation within the enzyme recognition sequence. The number of sites affected depends upon the dose of UV, thus making it easier to control the extent of enzyme digestion than by either limiting the digestion time, or the amount of enzyme. Restriction-site maps of bacteriophage lambda recombinants are readily produced by labelling DNA using a radioactive oligonucleotide that is complementary to either the left or right cohesive end of lambda, irradiating the DNA with UV light, limit digesting with the appropriate enzyme, and calculating the size of the fragments detected after gel electrophoresis and autoradiography.     

Size and physical map of the chromosome of Haemophilus influenzae.

A variation of pulse-field electrophoresis, field-inversion gel electrophoresis, was used to determine the size and physical map of the chromosome of Haemophilus influenzae. The DNA of H. influenzae had a low G + C content (39%) and no restriction sites for the enzymes NotI or SfiI. However, a number of restriction enzymes (SmaI, ApaI, NaeI, and SacII) that recognized 6-base-pair sequences containing only G and C nucleotides were found to generate a reasonable number of DNA fragments that were separable in agarose gels by field-inversion gel electrophoresis. The sizes of the DNA fragments were calibrated with a lambda DNA ladder and lambda DNA restriction fragments. The sum of fragment sizes obtained with restriction digests yielded a value for the chromosome of 1,980 kilobase pairs. Hybridization of a labeled fragment with two or more fragments from a digest with a different restriction enzyme provided the information needed to construct a circular map of the H. influenzae chromosome.     

λ噬菌体和Cosmid重组DNA克隆的快速限制性内切酶图谱分析方法

cosmld克隆的线性化用λcos末端酶来完成,线性的cosmid或λDNA经部份限制性内切酶酶解后,分别与已标记的cos顺序探针杂交(探针为分别与λ的左端或右端的cos顺序互补的12核苷酸单链片段),杂交后的部份酶解片段经电泳分离和自显影后,酶切点位置可直接在X-底片上读出。在本实验室条件下,可一次完成二个克隆包括5—6种限制性内切酶的图谱分析,分析和作图可通过计算机或手工进行。     

Preparation and FIGE separation of infrequent restriction fragments from Mycoplasma mycoides DNA

Use of procedures for obtaining satisfactory preparation and digestion of intact DNA of Mycoplasma mycoides subsp. mycoides Y in agarose blocks is reported. The use of inverted field agarose gel electrophoresis (FIGE) for separation of the small number of fragments derived from the genome by several restriction endonuclease digestions is shown. An effect that fragments containing replication forks remain in the well during FIGE, distorting the representative yield of restriction fragments on the gels, is overcome by incubating cells with chloramphenicol for 1 1/2 h before harvest to allow rounds of replication to go to completion without new initiations of DNA synthesis.     

A systematic study of field inversion gel electrophoresis.

The mobilities of oligomers of phage lambda DNA and of yeast chromosomes in agarose gels during field inversion gel electrophoresis (FIGE) were measured at different pulse times and electric fields. Also the ratios between forward and backward pulse times and/or field gradients were varied. The problem of 'band inversion' during FIGE, leading to an ambiguity in the mobility of large DNA fragments, was solved by using two dimensional gel electrophoresis with different parameters in the first and second dimension. The results are compared with those obtained with other pulsed electrophoresis systems and with a theoretical model.     

New cloning vectors and techniques for easy and rapid restriction mapping

We have modified plasmid, phage lambda and cosmid cloning vectors to be of general use for easily and unambiguously determining restriction maps of recombinant DNA molecules. Each vector is constructed so that it contains the rarely found NotI restriction site joined to a short synthetic linker sequence that is followed by a multiple cloning site. DNA cloned into these vectors may be restriction-mapped by either of two methods. In one technique, the cloned DNA is completely digested with NotI, followed by partial digestion with any other restriction enzyme. After electrophoresis and transfer to a nylon membrane, the fragments are hybridized to a labeled probe complementary to the NotI linker. In the second technique, referred to as recession hybridization detection, cloned DNA is digested with NotI and then briefly treated with exonuclease III to recess the 3' ends. After hybridizing a labeled complementary oligodeoxynucleotide to the single-stranded 5' end containing the linker sequence, the DNA is partially digested with another restriction enzyme, electrophoresed and the gel is exposed to x-ray film. With either method the size of each labeled fragment corresponds directly to the distance that a restriction site is located from the NotI linker terminus. Methods for obtaining partial restriction enzyme digests have been devised so that as many as 20 different enzymes may be conveniently mapped on a single gel in little more than a day. The vectors and techniques described may also be adapted to automated or semi-automated devices that read fragment lengths and calculate the resulting restriction map.(ABSTRACT TRUNCATED AT 250 WORDS)     

Physical maps of varicella-zoster virus DNA derived with 11 restriction enzymes

Varicella-zoster virus DNA was digested with 11 restriction endonucleases, and the resulting fragments were separated on agarose gels. Terminal fragments were identified by lambda exonuclease digestion. Physical maps were then constructed using a combination of double restriction enzyme digestion and hybridization to cloned BamHI fragments to place the remaining fragments in order.     

Linkage map of the fragments of herpesvirus papio DNA.

Herpesvirus papio (HVP), an Epstein-Barr-like virus, causes lymphoblastoid disease in baboons. The physical map of HVP DNA was constructed for the fragments produced by cleavage of HVP DNA with restriction endonucleases EcoRI, HindIII, SalI, and PvuI, which produced 12, 12, 10, and 4 fragments, respectively. The total molecular size of HVP DNA was calculated as close to 110 megadaltons. The following methods were used for construction of the map; (i) fragments near the ends of HVP DNA were identified by treating viral DNA with lambda exonuclease before restriction enzyme digestion; (ii) fragments containing nucleotide sequences in common with fragments from the second enzyme digest of HVP DNA were examined by Southern blot hybridization; and (iii) the location of some fragments was determined by isolating individual fragments from agarose gels and redigesting the isolated fragments with a second restriction enzyme. Terminal heterogeneity and internal repeats were found to be unique features of HVP DNA molecule. One to five repeats of 0.8 megadaltons were found at both terminal ends. Although the repeats of both ends shared a certain degree of homology, it was not determined whether they were identical repeats. The internal repeat sequence of HVP DNA was found in the EcoRI-C region, which extended from 8.4 to 23 megadaltons from the left end of the molecule. The average number of the repeats was calculated to be seven, and the molecular size was determined to be 1.8 megadaltons. Similar unique features have been reported in EBV DNA (D. Given and E. Kieff, J. Virol. 28:524-542, 1978).     

Assignment of Alu-repetitive sequences to large restriction fragments from human chromosomes 6 and 22

We have employed a pulsed field gel electrophoresis and Alu hybridization approach for identification of large restriction fragments on chromosome 6 and 22. This technique allows large portions of selected human chromosomes to be visualized as discrete hybridization signals. Somatic cell hybrid DNA which contains chromosome 6 or chromosome 22 was restricted with either Notl or Mlul. The restriction fragments were separated by pulsed field gel electrophoresis (PFGE) and hybridized against an Alu repetitive sequence (Blur 8). The hybridization signals result in a fingerprint-like pattern which is unique for each chromosome and each restriction enzyme. In addition, a continuous pattern of restriction fragments was demonstrated by gradually increasing puls times. This approach will also be suitable to analyze aberrant human chromosomes retained in somatic cell hybrids and can be used to analyze flow sorted human chromosomes. To this end, our method provides a valuable alternative to standard cytogenetic analysis.     

Electrophoretic mobility of high-molecular-weight, double-stranded DNA on agarose gels.

A new theoretical model for the migration of high-molecular-weight, double-stranded DNA on agarose gels is presented. This leads to the prediction that under certain conditions of electrophoresis, a linear relationship will exist between the molecular weight of a DNA molecule, raised to the (-2/3) power, and its electrophoretic mobility. Agarose gel electrophoresis of the fragments of bacteriophage lambda DNA produced by several restriction endonucleases confirms this relationship, and establishes some of the limits on its linearity. For this work, a polyacrylamide slab gel apparatus was modified for use with agarose gels. This apparatus has several advantages over others commercially available for agarose gel electrophoresis, including the abilities to run a larger number of samples at one time, to use lower-concentration gels, and to maintain better temperature stability across the width of the gel. The validation of the relationship developed here between molecular weight and electrophoretic mobility should make this a useful method for determining the molecular weights of DNA fragments.     

The interaction of E. coli integration host factor and lambda cos DNA: multiple complex formation and protein-induced bending.

The interaction of E. coli's integration Host Factor (IHF) with fragments of lambda DNA containing the cos site has been studied by gel-mobility retardation and electron microscopy. The cos fragment used in the mobility assays is 398 bp and spans a region from 48,298 to 194 on the lambda chromosome. Several different complexes of IHF with this fragment can be distinguished by their differential mobility on polyacrylamide gels. Relative band intensities indicate that the formation of a complex between IHF and this DNA fragment has an equilibrium binding constant of the same magnitude as DNA fragments containing lambda's attP site. Gel-mobility retardation and electron microscopy have been employed to show that IHF sharply bends DNA near cos and to map the bending site. The protein-induced bend is near an intrinsic bend due to DNA sequence. The position of the bend suggests that IHF's role in lambda DNA packaging may be the enhancement of terminase binding/cos cutting by manipulating DNA structure.     

Mapping genomic organization by field inversion and two-dimensional gel electrophoresis: application to the murine T-cell receptor gamma gene family.

A new two-dimensional gel electrophoresis technique has been developed for the mapping of multigene families. Resolution in the first dimension is based on the generation of large size DNA fragments by infrequently-cutting restriction enzymes, and separation of these fragments by field inversion gel (FIG) electrophoresis. A second restriction enzyme digestion is then carried out with the separated DNA fragments in the agarose gel. Standard gel electrophoresis in the second dimension allows one to estimate the number of hybridizing genes contained in each large DNA fragment. We have also developed a novel method to increase the separation, resolution and hybridization signal in the second dimension by condensing the bands from the first dimension into spots. As an example, we have applied these techniques to determine the organization of the murine T-cell receptor gamma locus. The murine gamma gene family was found to be contained on two DNA fragments encompassing 195 kilobases of DNA. The two-dimensional gel electrophoresis method is particularly useful in the analysis of the organization of multigenic families where single copy probes are not readily available, and should extend the potential usefulness of field inversion gel electrophoresis in gene mapping.     

Enhanced recovery and restriction mapping of DNA fragments cloned in a new lambda vector.

In this paper we describe a modification to the lambda vector EMBL3 which greatly expedites the construction of restriction maps of cloned DNA sequences. In the modified vector, EMBL3cos, all the phage coding sequences are placed to the right of the cloning sites so that the left cohesive end is separated by only 200bp, rather than 20kb (as in conventional lambda vectors), from the inserted DNA fragment. We show that reliable restriction maps can be rapidly constructed from partial digests of clones made in this vector by labelling the left cohesive end with a complementary 32P-labelled oligonucleotide. In addition, we quantify the restriction of clones containing human DNA by the McrA and McrB systems of E. coli and show that the use of Mcr- plating strains can increase the yield of recombinant phage up to tenfold, to give cloning efficiencies of greater than or equal to 10(7) pfu/microgram of human DNA.     

Rapid pulsed field separation of DNA molecules up to 250 kb.

Pulsed field gel electrophoresis (PFGE) is capable of resolving a wide size range of DNA molecules which would all co-migrate in conventional agarose gels. We describe pulsed field gel conditions which permit DNA fragments of up to 250 kilobases (kb) to be separated in only 3.5 h. The separations, which employ commercially available gel boxes, are achieved using conditions which deviate significantly from traditional pulsed field conditions. PFGE separations have been thought to require reorientation angles greater than 90 degrees to be effective. However, reorientation angles of 90 degrees and even less will resolve DNA fragments a few hundred kb and smaller approximately 5 x faster than with standard pulsed field conditions. The mobility of DNA fragments separated with 90 degrees reorientation angles is switch time-dependent, as is seen for DNA run with the commonly used reorientation angle of 120 degrees. With DNA fragments of several hundred kb and smaller, higher field strengths may be used, resulting in still greater increases in separation speed. The conditions described allow DNA from large insert bacterial clones, such as those using cosmid, Fosmid, P1, bacterial artificial chromosome (BAC), or P1-derived artificial chromosome (PAC) vectors, to be prepared, digested and analyzed on gels within a single working day.     

Versatile method employing basic techniques of genetic engineering to study the ability of low-molecular-weight compounds to bind covalently with DNA in cell-free systems

Numerous antitumor and carcinogenic compounds and free radicals are able to modify DNA by forming covalent bonds, mainly with nucleophilic centers in nucleobases. Such a binding is usually of utmost importance for the biological outcome. The level of DNA adducts formed by a given agent is in most cases extremely low; hence their detection is very difficult. Here we propose a simple approach, exploiting techniques widely used in genetic engineering, to demonstrate and characterize the covalent modification of a DNA fragment by any low-molecular-weight compound of interest in a cell-free system. The specifically designed, several-hundred-base-pairs-long double-stranded deoxyoligonucleotide (PCR amplified)--subject to modification--includes two restriction sites: one containing only GC base pairs recognized by restriction endonuclease MspI and the other including only AT base pairs recognized by restriction endonuclease Tru1I. The covalent modification of the restriction sites abolishes their recognition and thus cleavage by the endonucleases applied. The formation of DNA adducts is induced by incubating the oligonucleotide with increasing concentrations of a studied compound, in the appropriate activating system if required. Then, the modified oligonucleotide is submitted to digestion by the above-mentioned restriction endonucleases and the DNA fragments are separated by polyacrylamide gel electrophoresis. The inhibition of cleavage indicates the occurrence of covalent modification of the restriction site(s) while simultaneously pointing at the kind of base pairs involved in DNA adduct formation. The validation of the method was performed for two DNA binding antitumor compounds, cisplatin and CC-1065, which form adducts preferentially with guanine and adenine, respectively.     

Physical map of the bacteriophage T5 genome based on the cleavage products of the restriction endonucleases SalI, SmaI, BamI, and HpaI.

A physical map of the bacteriophage T5 genome was constructed by ordering the fragments produced by cleavage of T5 DNA with the restriction endonucleases SalI (4 fragments), SmaI (4 fragments), BamI (5 fragments), and HpaI (28 fragments). The following techniques were used to order the fragments. (i) Digestion of DNA from T5 heat-stable deletion mutants was used to identify fragments located in the deletable region. (ii) Fragments near the ends of the T5 DNA molecule were located by treating T5 DNA with lambda exonuclease before restriction endonuclease cleavage. (iii) Fragments spanning other restriction endonuclease cleavage sites were identified by combined digestion of T5 DNA with two restriction endonucleases. (iv) The general location of some fragments was determined by isolating individual restriction fragments from agarose gels and redigesting the isolated fragments with a second restriction enzyme. (v) Treatment of restriction digests with lambda exonuclease before digestion with a second restriction enzyme was used to identify fragments near, but not spanning, restriction cleavage sites. (vi) Exonucleases III treatment of T5 DNA before restriction endonuclease cleavage was used to locate fragments spanning or near the natural T5 single-chain interruptions. (vii) Analysis of the products of incomplete restriction endonuclease cleavage was used to identify adjacent fragments.     

Chain length determination of small double- and single-stranded DNA molecules by polyacrylamide gel electrophoresis.

We describe the use of polyacrylamide gel electrophoresis to estimate chain lengths of double- and single-stranded DNA molecules in the size range 20-1000 base pairs (or nucleotides). Double-stranded DNA molecules of known length produced either by organic synthesis or by restriction endonuclease digestion of viral DNAs were used as standards. The relative electrophoretic mobilities of these standards were examined on both nondenaturing (aqueous) polyacrylamide gels and on denaturing gels containing 7 M urea or 98% formamide. Electrophoretic mobility of DNA is a linear function of the log of molecular weight if appropriate conditions are used, although exceptions are noted. Chain lengths can be conveniently estimated by using as standards bacteriophage gamma DNA restriction fragments or commercially available tracking dyes.